Light emitting diodes (LEDs) generally emit light in a specific color or range of wavelengths. To produce a white light, it is usually necessary to combine or mix the light from multiple LEDs which emit different colors, for example, red, green and blue. Initially, light mixing was accomplished by placing LEDs of different colors next to each other such that the light emitted by each LED would mix with the light from the others. A common structure associated with such mixing is a light guide. This approach has several drawbacks including poor color mixing, uneven light intensity, and the presence of dark regions near the edges of the light guide plate.
Several techniques exist to improve the light mixing needed to produce white light. One is the insertion of LEDs in a mixing cavity within the light guide. Another is the use of a light diffusant layer to mix the colors. However, known light diffusant layers significantly reduce output of the light sources. While these techniques have resulted in slightly better color mixing, there remains a need for further improvement.